1. Field of the Invention
The present invention relates to a blade assembly that can be assembled into a medical device that is used to cut a cornea.
2. Prior Art
There have been developed a number of different surgical techniques to correct hyperopic or myopic conditions of a human eye. U.S. Pat. No. 4,840,175 issued to Peyman discloses a procedure wherein a thin layer of the cornea tissue is cut and removed from the cornea. A laser beam is then directed onto the exposed corneal tissue in a predetermined pattern. The laser beam ablates corneal tissue and changes the curvature of the eye. This procedure is sometimes referred to as Laser in situ Keratomileusis (LASIK).
U.S. Pat. No. Re 35,421 issued to Ruiz et al. discloses a device for cutting a cornea in a LASIK procedure. Such a device is commonly referred to as a microkeratome. The Ruiz microkeratome includes a ring that is placed onto a cornea and a blade that is located within an opening of the ring. The device also contains a drive mechanism which moves the blade across the cornea in a first direction while the blade moves in a reciprocating transverse direction to cut the eye. The device can create a lamella flap of the cornea which is flipped back so that the stromal bed of the cornea can be ablated with a laser.
U.S. Pat. No. 6,051,009 issued to Hellenkamp et al. discloses a microkeratome that is sold under the trademark HANSATOME. The HANSATOME microkeratome moves the blade in an arcuate path about the cornea. The HANSATOME includes a disposable blade assembly that can be readily loaded and removed from the device. The blade assembly includes a blade holder that is attached to a cutting blade. The blade holder has a recess that receives the end of a drive shaft. Rotation of the output shaft both moves the blade in an arcuate path and moves the blade in a back and forth motion to create the lamella flap of the cornea.
It is critical to control the depth of the cut to prevent a deep or shallow cut of the cornea. The depth of the cut is a function of the distance between the cutting edge of the blade and a reference surface of the blade holder. The HANSATOME blade holder is attached to the cutting blade by a pair of plastic protrusions that extend from the blade holder through corresponding apertures of the blade. The plastic protrusions located on the underside of the blade holder are then ultrasonically welded to the top side of the blade. The accuracy of the distance between the cutting edge and the reference surface, and thus the depth of the cut into the cornea, is dependent upon the mechanical tolerance between the cutting edge and the aperture of the blade, and the mechanical tolerance between the protrusions and the reference surface of the blade holder. This tolerance “build up” can reduce the predictability of the cutting depth. It would be desirable to provide a blade assembly and process for assembling the blade assembly that would tightly control the tolerance between the cutting edge and the reference surface and thus the depth of the cut.